Yay, finally our Trigonometry final is almost here. I'm taking the test this tuesday, and have been reviewing today.(adsbygoogle = window.adsbygoogle || []).push({});

One thing I've had a lot of trouble with is finding the correct sign on problems where I have to rewrite a trigonometric identity in terms of another.

For example:

Write tanx in terms of sinx, x is in Quadrant 4.

tanx = -sinx/cosx (-sinx because sinx is negative in Q4)

tanx = -sqrt(-sinx/sqrt(1-sin^{2}x)

I am assuming sinx is negative because it is in Quadrant 4. Yet the answer in the book says the fraction is positive.

Yet...

Write tanx in terms of cosx; x in Quadrant 2:

this should have negative cosine values so

tanx = -sqrt(1-cos^{2}x)/cosx is a correct answer in the back of the book.

Can anyone clarify anything about rewriting these with the correct sign values?

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# Homework Help: Rewriting in terms of another (Trigonometry)

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